Metathesis catalyst and process

ABSTRACT

The invention provides a method of preparing a metathesis catalyst, the method including the steps of mixing a transition metal oxide containing aqueous solution having a pH of 9 or higher with a carrier. The water is then removed from the mixture by means of evaporation to provide a metathesis catalyst.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a metathesis catalyst, a method of preparing ametathesis catalyst, a metathesis process and a product produced by themetathesis process.

BACKGROUND TO THE INVENTION

Metathesis, also known as olefin disproportionation, is a well-knownprocess for facilitating carbon transfer between or among one or moreolefins of an olefinic feed stream. Metathesis is a commerciallyvaluable method for converting lower value olefinic streams into highervalue olefinic streams. For example, the first and well-known metathesisprocess, the Triolefin process of Phillips Petroleum Co., was developedfor transforming a stream of short chained olefins comprising propyleneinto a higher value stream of ethylene and 2-buthene using WO₃ on asilica (SiO₂) carrier as a catalyst. It is known that, with the use ofcatalysts other than WO₃/SiO₂, a 1-pentene stream can be transformedinto a stream of 4-octene, with high selectivity, and ethylene using amolybdenum nitrosyl or carbonyl complex as a catalyst. The metathesis oflonger chained C₆ olefins and even higher has been disclosed in U.S.Pat. No. 5,162,597 using WO₃ on an AL₂O₃ carrier as a catalyst.

The known method of preparing WO₃/SiO₂ catalyst comprises wetimpregnation by adsorbing negatively charged oxyanion polytungstate ontosilica gel. The silica gel can be polarised or positively charged bylowering the pH to below its iso-electric point of between about 1 and2. It has been shown that a variety of tungsten oxyanion speciescontaining one, six and twelve tungsten atoms can be present in aqueoussolution, which can be controlled, to some extent, by the pH of thesolution. At a pH of below about 6, a six and twelve tungsten atomspecies are dominant and below a pH of about 4 a twelve tungsten speciesis dominant. The applicants have found that the active tungsten sites ofthe WO₃/SiO₂ catalysts prepared at a low pH are randomly distributed onthe surface of the SiO₂ and that clusters are formed at high loading ofWO₃ loading of more than about 6 wt % on SiO₂. These clusters areinactive for metathesis. The applicants further found that,disadvantageously, that catalysts prepared at pH below the iso electricpoint have a low conversion and selectivity towards linear olefin orprimary metathesis products of the metathesis of longer chained olefinicfeed streams. The applicants also found that WO₃ loading of more thanabout 6 wt % on SiO₂, provides no significant increase in conversionrate although it leads to a lower selectivity, due to increased Brφnstedacidity, towards linear olefin products or primary metathesis productsof the metathesis of longer chained olefinic feed: streams. Theformation of secondary metathesis products is a result of isomerisationof the olefinic feed stream followed by metathesis. It is thereforeimportant to lower the degree of Brφnsted acidity in order to limit theisomerisation reactions.

For linear alpha-olefinic feed streams, primary metathesis product shallbe understood to be linear olefins having 2n−2 carbons with the doublebond at the n−1 position, with n being the carbon number of thepredominant linear alpha olefin of the olefinic feed stream.

A further disadvantage of these catalysts are the relatively highoperating temperatures of up to 600° C., which lead to side reactionssuch as cracking, oligomerization, aromatisation, dehydrogenation etc.

However, these catalysts have certain inherent advantages over othercommercially available metathesis catalysts like MoO₃/Al₂O₃ andRe₂O₇/Al₂O₃ that makes it attractive for commercial applications.Firstly, it has a considerable resistance to poisons as might beexpected from the high operating temperatures, typically between300-600° C., secondly it has a long on-line lifetime compared to Mo- andRe-based metathesis systems, due to its resistance to poisons, andthirdly it can be regenerated without negative effect on catalyststructure.

It is therefore an object of this invention to provide a WO₃/SiO₂metathesis catalyst having all of its inherent advantages together witha relatively high conversion rate and selectivity, and an improved andoptimised metathesis process using such a catalyst.

An example of an attractive application of such a WO₃/SiO₂ metathesiscatalyst is a conversion process of alpha-olefins (C₅ to C₁₀), intolonger chain, higher value olefins.

GENERAL DESCRIPTION OF THE INVENTION

According to a first aspect of the invention there is provided acatalyst for metathesis of an olefinic feed stream, which includes:

a transition metal oxide; and

a carrier, the transition metal oxide being deposited onto the carrierfrom an aqueous solution of tungstate anions at a pH of more than about9.

The transition metal oxide may be tungsten oxide and the carrier may besilica.

It will be appreciated that the deposits form the catalytically activesites on the carrier.

The tungsten oxide may be deposited onto the carrier from an aqueoussolution of tungstate anions at a pH of more than about 10.

The tungsten oxide may be deposited onto the carrier from an aqueoussolution of tungstate anions at a pH of about 12.

The catalyst may be a heterogeneous catalyst.

The catalyst may further be characterised in that the tungsten oxidedeposits are substantially uniformly distributed on the surface of thecarrier.

The catalyst may even further be characterised in that most of thetungsten oxide deposits are substantially amorphous.

The catalyst may also be characterised in that at least a portion ofsome of the tungsten oxide deposits are in the form crystallites of lessthan about 135 Å across on the surface of the carrier.

The tungsten oxide may be from about 4 to 10 wt % on SiO₂.

The tungsten oxide may be from about 5 to 8 wt % on SiO₂.

According to a second aspect of the invention, there is provided amethod of preparing a metathesis catalyst, the method including thesteps of:

mixing a transition metal oxide containing aqueous solution having a pHof about 9 or higher with a carrier; and

removing water from the mixture by means of evaporation.

The transition metal may be silica and the transition metal may betungsten.

The aqueous solution may contain tungsten in the form of ammoniummetatungstatehydrate and/or ammonium tungstate.

The concentration of the ammonium metatungstatehydrate and the mass ofthe silica may be selected such that the WO₃ on the SiO₂ is from about 4to 10 wt %.

The concentration of the ammonium metatungstatehydrate and the mass ofthe silica may be selected such that the WO₃ on the SiO₂ is from about 5to 8 wt %.

The aqueous solution of ammonium metatungstatehydrate may have a pH ofmore than about 10.

The aqueous solution of ammonium metatungstatehydrate may have a pH ofabout 12.

Excess water may be removed by evaporation at about 80° C. under reducedpressure. It will be appreciated that the temperature and pressure maybe substantially varied to evaporate the excess water.

Further water may be removed after removal of the excess water by dryingthe residue at about 110° C. for about 12 hours, then by raising thetemperature at a rate of about 1° C. every minute up to about 250° C.,maintained at about 250° C. for about two hours and then by raising thetemperature at a rate of about 3° C. every minute up to about 550° C.

The residue may then be calcined at about 550° C. for about 8 hours.

It will also be appreciated that for the removal of further water andthe calcination the temperature and time may be substantially varied andsubstantially the same result obtained.

The calcination step substantially removes NH₃, ensures that theoxidation state of the tungsten is mostly 6+ and ensures that thetungsten oxide is bound to the carrier.

The pH of the aqueous solution may be adjusted before or during themixing step by adding an acid such as nitric acid or by adding an alkalisuch as ammonium hydroxide.

According to a third aspect of the invention, there is provided ametathesis process, which includes the step of:

contacting a C₅ and/or higher olefinic feed stream with a catalyst formetathesis as described above at a temperature of between about 350° C.and 600° C.

The process may include a step of activating the catalyst at about 500to 700° C. for about 8 hours in an inert atmosphere.

The olefinic feed stream may be selected such that the process yieldsC₁₀ to C₁₈ olefins. The C₁₀ to C₁₈ olefins are also known as thedetergent range olefins and may be used to manufacture detergents,diesels, drilling fluids, synthetic lubricants and other down streamproducts. The feed stream may include C₅ to C₁₀ alpha olefins.

The feed stream may be contacted with the catalyst at a LHSV (ml feed/mlcatalyst.h⁻¹ liquid hourly space velocity) of between about 5 and 25 h⁻¹at a temperature of between about 350 and 550° C. Preferably, the feedstream may be contacted with the catalyst at a LHSV of between about 10to 20 h⁻¹ at a temperature between about 420 and 500° C. The feed streammay include a C₅ to C₁₀ alpha olefin or mixtures thereof.

The feed stream may be contacted with the catalyst at a pressure of 100Pa to 1 mPa, preferably between about 1 and 100 kPa, thus preferablybetween 0.1 atm to 10 atm.

Using the higher pH instead of the known low pH during the production ofthe catalyst has the following advantages. Firstly, it facilitates anuniform distribution of the active tungsten sites deposited on thecarrier and secondly it lowers the Brφnsted acidity of the catalyst. Theuniform distribution of the deposits improves the conversion rate, whichin turn allows for a lower WO₃ loading, which in turn also lowers theBrφnsted acidity and the lower Brφnsted acidity in turn improves theselectivity of the catalyst towards linear olefin or primary metathesesproducts, particularly which of the metathesis of longer chainedolefinic feed streams. These advantages are in addition to a WO₃/SiO₂catalyst's inherent advantages.

According to a fourth aspect of the invention, there is provided aproduct produced by the process described above.

The product may include C₈ to C₂₀ internal olefins. The C₈ to C₂₀internal olefins may be mostly linear.

The feed stream may predominantly be a linear alpha-olefin and theproduct may comprise of at least 4% of a corresponding primarymetathesis product and at least 40% of a linear olefin product.

DETAILED DESCRIPTION OF THE INVENTION

The invention is now described by way of example using 1-octene and1-heptene as representative of olefinic feed streams.

It shall be understood that the examples are provided for illustratingthe invention further and to assist a person skilled in the art withunderstanding the invention and are not meant to be construed as undulylimiting the reasonable scope of the invention.

Preparation of a Metathesis Catalyst:

Silica gel, Davisil grade 646 (surface area: 300 m²/g, pore volume: 1.15cm³/g) was used as a carrier. A WO₃/SiO₂ precursor with a loading of 8wt % WO₃ was prepared by wet impregnation of the silica carrier (13.8 gSiO₂) with an aqueous solution of ammonium metatungstatehydrate(Aldrich, 99.9%) of appropriate concentration (1.2752 g or 0.000431moles of ammonium metatungstatehydrate). The pH of the aqueous solutionof ammonium metatungstatehydrate (Aldrich, 99.9%) was adjusted to about12 with the addition of either HNO₃ (Rochelle Chemicals, 55% chemicallypure) or Ammoniumhydroxide (25% NH₄OH solution in water). The solutionwas stirred for 48 hours. This solution was then added to the carrierand the pH adjusted again. The mixture was stirred for 2 hours and theexcess water was then removed by evaporation at 80° C. under reducedpressure. The residue was dried at 110° C. for 12 hours. The temperaturewas then raised at a rate of 1° C./min to 250° C. This temperature wasmaintained for 2 hours and then raised by 3° C./min to 550° C. The finalstep was a calcination step at 550° C. for 8 hours under an airatmosphere.

Catalysts with different tungsten metal loadings were prepared i.e. 3,4.5, 6, 7, 8, 10, 15 and 20 wt % of WO₃ on SiO₃. These catalysts arecharacterised in Table 1. TABLE 1 Actual Avg. Composition Surface PorePore (wt % Area Volume Size Crystallite Catalyst WO₃) (m²/g) (cm³/g)(nm) Size (Å)   3% WO₃/SiO₂ 2.8 326 1.11 13.7 N/A 4.5% WO₃/SiO₂ 4.1 3241.16 14.1 N/A   6% WO₃/SiO₂ 5.5 312 1.12 14.1 N/A   7% WO₃/SiO₂ 6.8 2871.04 14.0 N/A   8% WO₃/SiO₂ 8.0 252 0.98 15.6 126.0  10% WO₃/SiO₂ 9.9276 0.99 13.9 134.1  15% WO₃/SiO₂ 14.2 267 0.96 14.0 141.3  20% WO₃/SiO₂19.7 234 0.85 14.2 151.0Optimisation of a Metathesis Catalyst Using 1-octene as a RepresentativeFeed Stream:

Table 2 gives a summary of the conversions and product selectivitiesobtained with WO₃/SiO₂ metathesis catalysts with different WO₃ loadingsusing 1-octene as feed. All reactions were on-line for 8 hours andresults are reported as averages over the 8-hour period. Reactionconditions were 460° C., 5.6 h⁻¹ LHSV and atmospheric pressure. TABLE 2WO₃ Loading/% 3 4.5 6 7 8 10 15 20 C₈ Conversion/ 56.8 78.9 88.6 87.188.4 88.3 88.3 88.4 % Selectivity C₁₄ 15.2 7.3 5.3 4.8 4.6 4.2 4.0 4.0Linear/% Selectivity C₁₄ 0.6 0.5 0.5 0.5 1.0 0.9 0.9 0.8 Branched/%Selectivity 46.4 47.7 45.5 44.0 40.0 40.7 40.0 39.5 C₉₋₁₃ Linear/%Selectivity 1.6 2.2 2.6 2.7 5.7 5.8 5.4 5.3 C₉₋₁₃ Branched/%

Graph 1 shows the relationship between WO₃ loading and C₈ conversion. Itcan be seen from Graph 1 that that WO₃ loading of more than about 6% wt% provides no significant increase in conversion.

Graph 2 shows the relationship between conversion and time (hours) forcatalysts with different WO₃ loadings. It can be seen from Graph 2 thatcatalysts having a WO₃ loading of less than about 4.5% wt % experiencesignificant poisoning.

These results indicate an optimum WO₃ loading where selectivity tolinear metathesis products is high, branched product formation isrelatively low and catalyst lifetime is high. This optimum appear to bein the region of between 6 and 8 wt % WO₃.

Graph 3 shows the effect of the variation of the pH during impregnationon catalyst selectivity towards primary metathesis products.

Tunnelling electron microscope analysis showed improved dispersion ofWO₃ on the carrier with catalysts prepared with an aqueous solution at ahigh pH (pH10-12). More crystallites and an even or, in other words,uniform dispersion over the silica carrier was observed at a higher pHimpregnation and Table 3 gives crystallite size determinations. TABLE 3pH of impregnation Crystallite Catalyst solution Size (A) 8% WO₃/SiO₂ 1260.0 8% WO₃/SiO₂ 5 126.0 8% WO₃/SiO₂ 12 110.0

Table 4 gives a summary of the conversions and product selectivitiesobtained with WO₃/SiO₂ metathesis catalysts prepared by impregnating asilica carrier at different pH's, using 1-octene as feed. Impregnationat a higher pH resulted in increased production of linear metathesisproducts. The largest Improvement was observed with the production ofthe primary linear C₁₄ metathesis product. The linear secondarymetathesis products also show an improvement with a higher pH. Thereduction in branched metathesis products can be attributed to poisoningof some of the Brφnsted acidity necessary for skeletal isomerisation dueto the basic environment during preparation. TABLE 4 pH 1 3 5 8 10 12Conversion/% 88.5 88.7 88.2 88.2 87.6 85.5 C₉-C₁₃ 1.9 1.8 1.8 1.8 1.71.3 Branched C₉-C₁₃ Linear 46.0 45.3 46.5 45.6 48.7 49.0 C₁₄ branched0.3 0.3 0.3 0.3 0.3 0.2 C₁₄ linear 5.3 5.3 5.3 5.4 6.0 8.2An example of Using the Optimised Catalyst in a Metathesis Process usinga Feed Stream of 1-heptene:

Scheme 1 shows a plant equipped with the necessary work-up facilitiesand recycle lines for metathesis.

Column 1 includes a reboiler set at 220° C., Column 2 includes acondenser set at 25° C. and Reboiler set at 34° C. The Recycle line isset at 25° C., and the Reactor temperature is 460° C. The LHSV is 16 h⁻¹(including a recycle loop of C₅-C₁₀ at a 1:5.6 ratio) and the Reactorpressure is 10 kPa_(g), thus 0.1 atm. A C₇ single linear olefin streamwas used as a feed stream to the reactor. The composition In mass % ofthe feed stream is depicted in Table 5. TABLE 5 3-Me-3-hexene 0.09845-Me-1-hexene 0.0610 4-Me-1-hexene 0.2029 2-Me-1-hexene 1.00002-Methylhexane 0.4711 3-Methylhexane 1.5997 1-heptene 74.6147 n-heptane13.3506 2-methyl-2-hexene 1.0000 3-Heptene 1.1094 diene or cyclic olefin1.4993 2-Heptene 2.9874 Dienes or cyclic olefins ca 2.00

An 8 wt % WO₃/SiO₂ catalyst (0.3 mm average particle size, 20 ml) wasloaded into a tubular fixed bed reactor (25.4 mm diameter). Thiscatalyst was pre-treated at 550° C. under air (12 hours), followed bytreatment at the same temperature with molecular nitrogen (12 hours)before allowing the catalyst to cool down under an inert atmosphere tothe operating temperature (460° C.). The feed was introduced at 0.8ml/min and the recycle line (containing the C₅-C₁₀ fraction) wasoperated at 4.5 ml/min. Samples of the purge stream, gas stream andheavy product (see Scheme 1) was analysed every 12 hours via a gaschromatograph. This was continued for 700 hours and the processterminated. The same catalyst was regenerated by a calcination step at550° C. for 8 hours under an air atmosphere and a second run wasstarted. The second run was continued for 1200 hours. In both cases, thecatalyst was still active at the point of termination. A summary of theresults obtained can be found in Table 6. Values presented are anaverage over 80% of the run duration, ignoring first and last 10% of therun. Ethylene purity is expressed as % ethylene in themethane—ethane—ethylene fraction. Propylene purity is expressed as %propylene in the propane—propylene fraction. The primary metathesisproducts of heptene are ethylene and dodecene, olefins formed outsidethis range can be referred to as secondary metathesis products. Thisvalue gives an indication of the ratio between isomerization offeed/product and metathesis on the catalyst surface. TABLE 6 Run 1 Run 2Online time (hours) 700 1200 Total feed conversion (%) 88.2 84.7Selectivity (%) to Ethylene 7.56 8.52 Propylene 4.74 4.05 Undecene (C₁₁)12.03 12.81 Dodecene (C₁₂) 41.28 46.25 Tri-and Tetradecene (C₁₃-C₁₄)7.62 5.55 Ethylene Purity (%) 98.92 99.27 Propylene Purity (%) 98.8598.97 Linearity of C₁₂ (%) 97.0 97.0 % Primary metathesis 65.3 66.6 MassBalance (%) 89.4 95.1

The values of the two runs depicted in Table 6 are very similar. Therewas however a slight drop in conversion with the regenerated catalyst,but the selectivity towards the detergent range C₁₁ and C₁₂ increasedwith the regenerated catalyst.

The high linearity index of the dodecene is advantageous for exampleused in detergent synthesis. For linear alkyl benzenes synthesis thedodecene should be highly linear.

Optimising the Above Example Process using as an Example, a Feed Streamof 1-heptene:

By using the abovementioned optimised catalyst together with theoptimised conditions the applicant managed to keep the catalyst on-linefor 1200 hours without losing any significant activity or anysignificant indication of catalyst deactivation. The catalyst istherefore capable of running for longer than 1200 hours. Prior art workdone on short-chain olefins (C₂-C₄) only managed a maximum of 40%conversion that could be kept constant for 60 hours before deactivationstarted to occur. (E. D. Oliver, Butylenes, Process Economics ProgramSRI Report, October 1971, Report No 71)

Optimisation of reaction conditions with respect to pressure,temperature and contact time of the feed stream with catalyst (LHSV) isequally as important as developing and optimising the right catalyst fora specific chemical transformation.

Optimising Temperature and LHSV

Graph 4 shows that, with an 8 wt % WO₃/SiO₂ catalyst, by increasing thetemperature and decreasing the LHSV at 10 kPa_(g), the conversion can beincreased. However, due to side reactions, the conversion observed isnot necessarily conversion towards metathesis products. Temperature andLHSV alone should therefore not be used to find the optimised reactionconditions.

The applicant also realised that selectivity towards the C₁₁-C₁₄ rangecan also result in the wrong optimised reaction conditions, asselectivity does not take the conversion into account. A highselectivity can be obtained with a low conversion, which means that afairly high recycle stream to feed stream ratio must be employed whichmay not make economical sense. The applicant found that a high LHSV andlow temperature must be employed in order to give the highestselectivity towards a C₁₁-C₁₄ range, see Graph 5. Taking into accountthe low conversion under these conditions, the applicant concluded thatselectivity towards a C₁₁-C₁₄ range should not be used as a probe forcondition optimisation.

However, the yield towards C₁₁-C₁₄ on the other hand does incorporateboth conversion and selectivity as can be seen from equation 1.$\begin{matrix}{{Yield} = \frac{{Conversion} \times {Selectivity}}{100}} & (1)\end{matrix}$

By using yield towards the C₁₁-C₁₄ range, the applicant was able toarrive at a solution for the reaction condition optimisation. This wasdone through a three-stage design as depicted in Graph 6, giving thedirection of increase over each design block. The result of acombination of all three design blocks can be seen in Graph 7, resultingin an optimum yield at 460° C. and a total LHSV of 16 h⁻¹.

Optimising Temperature, LHSV and Pressure.

The applicant realised that an increase in pressure causes and increasein contact time of the feed with the catalyst and effectively decreasingthe LHSV and as thus it may be appreciated that an increase in pressureon the system would lower the yield. This was indeed found to be thecase as depicted in Graph 8 (units in Graph 8 indicated as atmosphericpressure). Although a pressure below atmospheric pressure will provide abetter yield, economical and practical considerations prompted theapplicant to choose atmospheric pressure as an optimum.

The applicant therefore found that the optimum yield towards the C₁₁-C₁₄range can be obtained by working at a temperature of 460° C., a LHSV of16 h⁻¹ and 10 kPa_(g) pressure, thus 1 atm.

Table 7 gives a comparison of experimental results of a 6 wt % WOSiO₂catalyst with the 8 wt % WO₃/SiO₂ catalyst over a 48 hour period at theabovementioned optimised conditions. TABLE 7 Catalyst 8% WO₃/SiO₂ 8%WO₃/SiO₂ LHSV 16 16 Conversion/% 54.2 71.3 Selectivity C₉-C₁₃ Branched/%1.9 1.8 Selectivity C₉-C₁₃ Linear/% 47.6 47.3 Selectivity C₁₄ Branched/%0.2 0.2 Selectivity C₁₄ Linear/% 14.7 15.2 % Branched C₉-C₁₃ 4.1 3.9 %Branched C₁₄ 1.4 1.4

1-25. (canceled)
 26. A method of preparing a metathesis catalyst, themethod including the steps of: mixing an aqueous solution of transitionmetal anions having a pH of 9 or higher with a carrier; and removingwater from the mixture by means of evaporation.
 27. A method as claimedin claim 26, wherein the carrier is silica and the transition metal istungsten.
 28. A method as claimed in claim 27, wherein the aqueoussolution contains tungsten in the form of ammonium metatungstatehydrateand/or ammonium tungstate.
 29. A method as claimed in claim 38, whereinthe aqueous solution contains tungsten in the form of ammoniummetatungstatehydrate and wherein the concentration of the ammoniummetatungstatehydrate and the mass of the silica are selected such thatthe WO₃ on the SiO₂ is from 4 to 10 wt %.
 30. A method of preparing ametathesis catalyst as claimed in claim 26, wherein excess water isremoved by evaporation at about 80° C. under reduced pressure to form aresidue.
 31. A method of preparing a metathesis catalyst as claimed inclaim 30, wherein further water is removed after removal of the excesswater by drying the residue at about 110° C. for about 12 hours, then byraising the temperature at a rate of about 1° C. every minute up toabout 250° C., maintained at about 250° C. for about two hours and thenby raising the temperature at a rate of about 3° C. every minute up toabout 550° C.
 32. A method of preparing a metathesis catalyst as claimedin claim 31, wherein the residue is then calcined.
 33. A method ofpreparing a metathesis catalyst as claimed in claim 32, wherein theresidue is calcined at about 550° C. for about 8 hours.
 34. A method ofpreparing a metathesis catalyst as claimed in claim 32, wherein theresidue is calcined at a temperature and for duration such that thecalcination step substantially removes NH₃, ensures that the oxidationstate of the tungsten is mostly 6+ and ensures that the tungsten oxideis bound to the carrier.
 35. A catalyst for metathesis of an olefinicfeed stream, which includes: a transistion metal oxide; and a carrier,the transition metal oxide being deposited onto the carrier from anaqueous solution of transition metal oxide anions at a pH of 9 or more.36. A catalyst as claimed in claim 35, wherein the transition metal istungsten and the carrier is silica.
 37. A catalyst as claimed in claim35, wherein the catalyst is a heterogeneous catalyst.
 38. A catalyst asclaimed in claim 36, wherein the catalyst is a heterogeneous catalyst.39. A catalyst as claimed in claim 37, wherein most of the tungstenoxide deposits are substantially amorphous.
 40. A catalyst as claimed inclaim 38, wherein most of the tungsten oxide deposits are substantiallyamorphous.
 41. A catalyst as claimed in claim 36, wherein the catalystis characterised in that at least a portion of some of the tungstenoxide deposits are in the form crystallites of less than about 135 Åacross on the surface of the carrier.
 42. A catalyst as claimed in claim36, wherein the tungsten oxide is from about 4 to 10 wt % on SiO₂.
 43. Acatalyst as claimed in claim 36, wherein the catalyst is characterisedin that it remains catalytically active for at least 1000 hours atoptimal operating conditions.
 44. A catalyst as claimed in claim 36,wherein the catalyst is characterised in that it provides a conversionrate of at least 30% for at least 50 hours at optimal operatingconditions.
 45. A metathesis process, which includes the step of:contacting a C₅ and/or higher olefinic feed stream with a catalyst formetathesis at a temperature of between 350° C. and 600° C., whichcatalyst includes: a transistion metal oxide; and a carrier, thetransition metal oxide being deposited onto the carrier from an aqueoussolution of transition metal oxide anions at a pH of 9 or more.
 46. Ametathesis process as claimed in claim 45, wherein the transition metalis tungsten and the carrier is silica.
 47. A metathesis process asclaimed in claim 45, wherein the process includes a step of activatingthe catalyst about 500 to 700° C. for about 8 hours in an inertatmosphere.
 48. A metathesis as claimed in claim 47, wherein theolefinic feed stream is selected such that the process yields C₁₀ to C₁₈olefins.
 49. A metathesis process as claimed in claim 45, wherein thefeed stream is contacted with the catalyst at a LHSV of between 5 and 25h⁻¹ at a temperature of between 350 and 550° C.
 50. A metathesis processas claimed in claim 45, wherein the feed stream is contacted with thecatalyst at a pressure of 0.1 to 10 atm.